Resolvers are typically used in motor controls. A resolver has three inductively coupled coils, one of which is carried by the rotor and the two other are arranged on the stator as mutually shifted by 90°. With each of the stator coils the rotor coil forms a transformer with a transmission coefficient that depends on the relative rotational position. A sinusoidal carrier signal is applied to the rotor coil, and so the stator coils provide amplitude modulated wave signals with a mutual phase shift of 90°, one of which is referred to as a sine wave and the other as a cosine wave signal. The angular position of the rotor is obtained by evaluating the sine and cosine wave signals.
For evaluation, the analog sine and cosine wave signals may be sampled with an analog-to-digital converter and processed digitally, applying an ‘arctan’ function. Available solutions are expensive, however.